The USP was originally
built around the .40S&W cartridge, but a
9x19mm Parabellum was introduced at the same time. In May 1995, Heckler &
Koch introduced a .45ACP variant. The USP Compact
series was introduced in 1996 and is available in 9 mm Parabellum, .40 S&W, .45
ACP, and, exclusively to the Compact model, .357 SIG.
Other variants of the standard USP include the USP Tactical, USP Expert, USP
Match, USP Elite and the standard sidearm of the
German Armed Forces (Bundeswehr) the P8.